Polymeric antioxidants

ABSTRACT

Antioxidant polymers of the present invention comprise repeat units that include one or both of Structural Formulas (I) and (II): 
                         
wherein:
         R is —H or a substituted or unsubstituted alkyl, acyl or aryl group;   Ring A is substituted with at least one tert-butyl group or substituted or unsubstituted n-alkoxycarbonyl group;   Ring B is substituted with at least one —H and at least one tert-butyl group or substituted or unsubstituted n-alkoxycarbonyl group;   Rings A and B are each optionally substituted with one or more groups selected from the group consisting of —OH, —NH, —SH, a substituted or unsubstituted alkyl or aryl group, and a substituted or unsubstituted alkoxycarbonyl group;   n is an integer equal to or greater than 2; and   p is an integer equal to or greater than 0.       
     The invention also includes methods of using and preparing these polymers.

RELATED APPLICATION

This application claims the benefit of U.S. Provisional Application No.60/370,468, filed on Apr. 5, 2002. The entire teachings of the aboveapplication are incorporated herein by reference.

GOVERNMENT SUPPORT

The invention was supported, in whole or in part, by a grant DMR-9986644from National Science Foundation. The Government has certain rights inthe invention.

BACKGROUND OF THE INVENTION

Synthetic antioxidant preservatives are added to a wide variety ofproducts during processing and storage. The types of products includefoods, plastics and packaging materials. When an oxidizing event takesplace in a product, the antioxidant molecules rapidly react to formantioxidant radicals. This reaction protects the product from damageresulting from the oxidizing event and consequently increases the shelflife of the product. Common synthetic antioxidant preservatives includebutylated hydroxyanisole (BHA), butylated hydroxytoluene (BHT),tert-butylhydroquinone (TBHQ), di-tert-butylhydroquinone (DTBHQ), andpropyl gallate. There are also naturally occurring antioxidants, whichinclude sesamol, sesamin, vitamin A and beta-carotene, vitamin E andtocopherols and vitamin C.

The use of antioxidant preservatives is particularly common in foodswith significant unsaturated lipid content. These foods also containquantities of unsaturated fatty acids. Unsaturation in fatty acids makeslipids susceptible to oxidation, which in turn leads to complex chemicalchanges in the lipids. These chemical changes eventually manifestthemselves in the development of off-flavors (rancidity) in foods. Theoxidation of unsaturated fatty acids is typically mediated by freeradicals, which can be caused by heat, light, ionizing radiation, tracemetals and some proteins. The use of antioxidant preservatives inlipid-containing foods minimizes rancidity, retards the formation oftoxic oxidation products, allows maintenance of nutritional quality andincreases the shelf life. The mechanism by which the antioxidantpreservatives are believed to act involves scavenging peroxyl radicalsand preventing propagation of the oxidation process. The antioxidantactivity of these compounds is lost upon scavenging a free radical, so afood or other product is no longer protected from oxidation once all theantioxidant preservative has reacted with a free radical. In otherwords, the degree of protection from oxidation depends on the quantityof antioxidant preservative that is present.

Unfortunately, there are restrictions on the amount of syntheticantioxidant preservatives that can be added to a product, especiallyproducts intended for human or animal consumption. The U.S. Food andDrug Administration limits the amount of BHA and BHT in foods to 0.02%of total fat, because these compounds are suspected to be carcinogenic.

Consequently, there is a need for a new class of synthetic antioxidantpreservatives that are less toxic to humans and animals. Also, it wouldbe advantageous to develop an antioxidant preservative with increasedpotency and the ability to be readily processed with a variety ofmaterials. Antioxidant preservatives with these improved propertieswould increase the shelf life and palatability of lipid-containing fooditems, as well as other products containing moieties (e.g., unsaturatedcarbon-carbon bonds) that can be damaged by free radicals.

SUMMARY OF THE INVENTION

In one embodiment, the present invention includes a method of inhibitingoxidation of a substance, comprising the step of contacting thesubstance with a substituted benzene antioxidant polymer. Preferably,the substituted benzene antioxidant polymer includes one or morehydroxyl or ether moieties per benzene.

In a preferred embodiment, the antioxidant polymer comprises repeatunits that include one or both of Structural Formulas (I) and (II):

where:

R is —H or a substituted or unsubstituted alkyl, acyl or aryl group;

Ring A is substituted with at least one tert-butyl group or substitutedor unsubstituted n-alkoxycarbonyl group, and optionally one or moregroups selected from the group consisting of —OH, —NH, —SH, asubstituted or unsubstituted alkyl or aryl group, and a substituted orunsubstituted alkoxycarbonyl group;

Ring B is substituted with at least one —H and at least one tert-butylgroup or substituted or unsubstituted n-alkoxycarbonyl group andoptionally one or more groups selected from the group consisting of —OH,—NH, —SH, a substituted or unsubstituted alkyl or aryl group, and asubstituted or unsubstituted alkoxycarbonyl group;

n is an integer equal to or greater than 2; and

p is an integer equal to or greater than 0.

In another embodiment, the present invention includes an antioxidantpolymer, comprising repeat units that include one or both of StructuralFormulas (I) and (II):

where:

R is —H or a substituted or unsubstituted alkyl, acyl or aryl group;

Ring A is substituted with at least one tert-butyl group or substitutedor unsubstituted n-alkoxycarbonyl group, and optionally one or moregroups selected from the group consisting of —OH, —NH, —SH, asubstituted or unsubstituted alkyl or aryl group, and a substituted orunsubstituted alkoxycarbonyl group;

Ring B is substituted with at least one —H and at least one tert-butylgroup or substituted or unsubstituted n-alkoxycarbonyl group andoptionally one or more groups selected from the group consisting of —OH,—NH, —SH, a substituted or unsubstituted alkyl or aryl group, and asubstituted or unsubstituted alkoxycarbonyl group;

n is an integer equal to or greater than 2; and

p is an integer equal to or greater than 0.

The antioxidant polymers can be part of a composition, such as acomposition comprising an edible product and an antioxidant polymer thatincludes repeat units represented by one or both of Structural Formulas(I) and (II):

where:

R is —H or a substituted or unsubstituted alkyl, acyl or aryl group;

Ring A is substituted with at least one tert-butyl group or substitutedor unsubstituted n-alkoxycarbonyl group, and optionally one or moregroups selected from the group consisting of —OH, —NH, —SH, asubstituted or unsubstituted alkyl or aryl group, and a substituted orunsubstituted alkoxycarbonyl group;

Ring B is substituted with at least one —H and at least one tert-butylgroup or substituted or unsubstituted n-alkoxycarbonyl group andoptionally one or more groups selected from the group consisting of —OH,—NH, —SH, a substituted or unsubstituted alkyl or aryl group, and asubstituted or unsubstituted alkoxycarbonyl group;

n is an integer equal to or greater than 2; and

p is an integer equal to or greater than 0.

Another composition is used for packaging and comprises a packagingmaterial and an antioxidant polymer that includes repeat unitsrepresented by one or both of Structural Formulas (I) and (II):

where:

R is —H or a substituted or unsubstituted alkyl, acyl or aryl group;

Ring A is substituted with at least one tert-butyl group or substitutedor unsubstituted n-alkoxycarbonyl group, and optionally one or moregroups selected from the group consisting of —OH, —NH, —SH, asubstituted or unsubstituted alkyl or aryl group, and a substituted orunsubstituted alkoxycarbonyl group;

Ring B is substituted with at least one —H and at least one tert-butylgroup or substituted or unsubstituted n-alkoxycarbonyl group andoptionally one or more groups selected from the group consisting of —OH,—NH, —SH, a substituted or unsubstituted alkyl or aryl group, and asubstituted or unsubstituted alkoxycarbonyl group;

n is an integer equal to or greater than 2; and

p is an integer equal to or greater than 0.

The present invention also includes a method of preparing an antioxidantpolymer, which comprises the step of polymerizing a monomer representedby Structural Formula (XIX):

where:

R is —H or a substituted or unsubstituted alkyl, acyl or aryl group; and

R₄, R₅, R₆, R₇ and R₈ are independently —H, —OH, —NH, —SH, a substitutedor unsubstituted alkyl or aryl group, or a substituted or unsubstitutedalkoxycarbonyl group, and

provided that:

-   -   (1) at least one of R₄, R₅, R₆, R₇ and R₈ is a tert-butyl group        or a substituted or unsubstituted alkoxycarbonyl group, and at        least two of R₄, R₅, R₆, R₇ and R₈ are —H; or    -   (2) at least one of R₄, R₅, R₆, R₇ and R₈ is a tert-butyl group        or a substituted or unsubstituted alkoxycarbonyl group, at least        one of R₄, R₅, R₆, R₇ and R₈ is a hydroxyl, alkoxy,        alkoxycarbonyl or aryloxycarbonyl group, and at least one of R₄,        R₅, R₆, R₇ and R₈ is —H.

The polymerization is typically catalyzed by an enzyme or an enzymemimetic capable of polymerizing a substituted benzene compound in thepresence of hydrogen peroxide.

One advantage of antioxidant polymers of the present invention is thatthey are expected to be less toxic or even non-toxic to animals, byvirtue of being largely unabsorbed. Also, these polymers are generallymore potent and exhibit greater thermal stability than small moleculeantioxidants, so that a smaller quantity of antioxidant is typicallyneeded to achieve the same protective effect. In addition, theantioxidant polymers can be blended into another polymeric material orcan form a thin film coating on the material, and unlike a smallmolecule antioxidant, diffusion out of the polymeric material will mostoften occur slowly. The invention also provides a largelyenvironmentally-safe method for preparing these antioxidant polymers.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a high resolution 500 MHz ¹H NMR spectrum of2-tert-butyl-4-hydroxyanisole (2-BHA).

FIG. 2 shows a high resolution 500 MHz ¹H NMR spectrum of enzymaticallypolymerized poly(2-BHA).

FIG. 3 shows the matrix assisted laser desorption ionizationtime-of-flight mass spectrum (MALDI-TOF-MS) of the poly(2-BHA), whichindicates that a distribution of polymeric species were formed.

FIG. 4 shows the comparative thermogravimetric analysis of 2-BHA andpoly(2-BHA).

FIG. 5 shows the matrix assisted laser desorption ionizationtime-of-flight mass spectrum (MALDI-TOF-MS) of thepoly(tert-butyl-hydroxyquinone) (poly(TBHQ)), which indicates that adistribution of polymeric species were formed.

FIG. 6 shows the antioxidant activity profile of 2-BHA and poly(2-BHA)at 100 ppm in the beta-carotene/linoleate model system described inExample 2.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is generally directed to a method of inhibitingthe oxidation of a substance, which involves contacting the substancewith a substituted benzene antioxidant polymer. The invention is alsodirected to the substituted benzene antioxidant polymers, variouscompositions containing such antioxidant polymers, and methods ofpreparing such antioxidant polymers.

For purposes of the present invention, a “method of inhibitingoxidation” is defined herein as a method that inhibits the propagationof a free radical-mediated process. Free radicals can be generated byheat, light, ionizing radiation, metal ions and some proteins andenzymes. Inhibiting oxidation also includes inhibiting reactions causedby the presence of oxygen, ozone or another compound capable ofgenerating these gases or reactive equivalents of these gases.

Repeat units of the antioxidant polymers of the invention includesubstituted benzene molecules. These benzene molecules are typicallybased on phenol or a phenol derivative, such that they have at least onehydroxyl or ether functional group. Preferably, the benzene moleculeshave a hydroxyl group. The hydroxyl group is not restricted to being afree hydroxyl group, and the hydroxyl group can be protected or have acleavable group attached to it (e.g., an ester group). Such cleavablegroups can be released under certain conditions (e.g., changes in pH),with a desired shelf life or with a time-controlled release (e.g.,measured by the half-life), which allows one to control where and/orwhen an antioxidant polymer is able to exert its antioxidant effect.

Substituted benzene repeat units of an antioxidant polymer of theinvention are also typically substituted with a bulky alkyl group or ann-alkoxycarbonyl group. Preferably, the benzene monomers are substitutedwith a bulky alkyl group. More preferably, the bulky alkyl group islocated ortho or meta to the hydroxyl group on the benzene ring. A“bulky alkyl group” is defined herein as an alkyl group that is branchedalpha- or beta- to the benzene ring. Preferably, the alkyl group isbranched alpha to the benzene ring. More preferably, the alkyl group isbranched twice alpha to the benzene ring, such as in a tert-butyl group.Other examples of bulky alkyl groups include isopropyl, 2-butyl,3-pentyl, 1,1-dimethylpropyl, 1-ethyl-1-methylpropyl and1,1-diethylpropyl. The bulky alkyl groups are preferably unsubstituted,but they can be substituted with a functional group that does notinterfere with the antioxidant activity of the molecule or the polymer.Straight chained alkoxylcarbonyl groups include methoxycarbonyl,ethoxycarbonyl, n-propoxycarbonyl, n-butoxycarbonyl andn-pentoxycarbonyl. n-propoxycarbonyl is a preferred group. Similar tothe bulky alkyl groups, n-alkoxycarbonyl groups are optionallysubstituted with a functional group that does not interfere with theantioxidant activity of the molecule or the polymer.

Preferred polymers of the present invention include repeat unitsrepresented by one or both of Structural Formulas (III) and (IV):

where Rings A and B are substituted as described above and n and p areas defined above.

Preferably, Ring A and Ring B in Structural Formulas (I) to (IV) areeach substituted with at least one tert-butyl group.

The polymer advantageously includes repeat units represented by one ormore of Structural Formulas (Va), (Vb), (Vc), (VIa), (VIb) and (VIc):

where R₁, R₂ and R₃ are independently selected from the group consistingof —H, —OH, —NH, —SH, a substituted or unsubstituted alkyl or arylgroup, and a substituted or unsubstituted alkoxycarbonyl group, providedthat at least one of R₁, R₂ and R₃ is a tert-butyl group; and j and kare independently integers of zero or greater, such that the sum of jand k is equal to or greater than 2.

In a preferred embodiment, R is —H or —CH₃; R₂ is —H, —OH, or asubstituted or unsubstituted alkyl group; or both.

Specific examples of repeat units included in polymers of the presentinvention are represented by one of the following structural formulas:

Advantageously, a polymer of the present invention consists of repeatunits represented by one or more of Structural Formulas (VII) to(XVIII).

Antioxidant polymers of the present invention are prepared bypolymerizing a molecule represented by Structural Formula (XIX):

Preferably, a molecule represented by Structural Formula (XIX) has one,two, three, four or five of the following features. In the firstfeature, at least one of R₅, R₇ and R₈ is a tert-butyl group. In thesecond feature, R₄ is —H. In the third feature, one or both of R₇ and R₈is —H. In the fourth feature, R is —H or —CH₃. In the fifth feature, R₆is —H, —OH or a substituted or unsubstituted alkyl group. Morepreferably, a molecule represented by Structural Formula (XIX) has thefirst and second features; the first, second and third features; thefirst, second, third and fourth features; or the first, second, third,fourth and fifth features.

Specific examples of monomers that can be polymerized to form anantioxidant polymer of the present invention are represented by one ofthe following structural formulas:

Antioxidant polymers of the present invention have two or more repeatunits, preferably greater than about five repeat units. The molecularweight of the polymers disclosed herein is generally selected to beappropriate for the desired application. Typically, the molecular weightis greater than about 500 atomic mass units (amu) and less than about2,000,000 amu, greater than about 1000 amu and less than about 100,000,greater than about 2,000 amu and less than about 10,000, or greater thanabout 2,000 amu and less than about 5,000 amu. For food or edibleproducts (e.g., products fit for human consumption), the molecularweight is advantageously selected to be large enough so that anantioxidant polymer cannot be absorbed by the gastrointestinal tract,such as greater than 1000 amu. For antioxidant polymers blended with apolymeric material, the molecule weight is advantageously selected suchthat the rate of diffusion of the antioxidant polymer through thepolymeric material is slow relative to the expected lifetime of thepolymeric material.

Antioxidant polymers of the present invention can be either homopolymersor copolymers. A copolymer preferably contains two or more or three ormore different repeating monomer units, each of which has varying oridentical antioxidant properties. The identity of the repeat units in acopolymer can be chosen to modify the antioxidant properties of thepolymer as a whole, thereby giving a polymer with tunable properties.The second, third and/or further repeat units in a copolymer can beeither a synthetic or natural antioxidant.

Antioxidant polymers of the present invention are typically insoluble inaqueous media. The solubility of the antioxidant polymers in non-aqueousmedia (e.g., oils) depends upon the molecular weight of the polymer,such that high molecular weight polymers are typically sparingly solublein non-aqueous media. When an antioxidant polymer of the invention isinsoluble in a particular medium or substrate, it is preferablywell-mixed with that medium or substrate.

Antioxidant polymers of the present invention can be branched or linear,but are preferably linear. Branched antioxidant polymers can only beformed from benzene molecules having three or fewer substituents (e.g.,three or more hydrogen atoms), as in Structural Formulas (XX), (XXI) and(XXIV).

Polymerization of the monomers is catalyzed by a natural or syntheticenzyme or an enzyme mimetic capable of polymerizing a substitutedbenzene compound in the presence of hydrogen peroxide, where the enzymeor enzyme mimetic typically have a heme or related group at the activesite. One general class of enzymes capable of catalyzing this reactionis commonly referred to as the peroxidases. Horseradish peroxidase,soybean peroxidase, Coprinus cinereus peroxidase, and Arthromycesramosus peroxidase are readily available peroxidases. Other enzymescapable of catalyzing the reaction include laccase, tyrosinase, andlipases. Suitable enzymes are able to catalyze the formation of acarbon-carbon bond and/or a carbon-oxygen-carbon bond between two aryl(e.g., phenyl, phenol) groups when a peroxide (e.g., hydrogen peroxideor an organic peroxide) is present. A subunit or other portion of aperoxidase is acceptable, provided that the active site of the enzyme isstill functional. Enzyme mimetics typically correspond to a part of anenzyme, so that they can carry out the same reaction as the parentenzyme but are generally smaller than the parent enzyme. Also, enzymemimetics can be designed to be more robust than the parent enzyme, suchas to be functional under a wider variety of conditions (e.g., differentpH range, aqueous, partically aqueous and non-aqueous solvents) and lesssubject to degradation or inactivation. Suitable enzyme mimetics includehematin, tyrosinase-model complexes and iron-salen complexes. Hematin,in particular, can be functionalized to allow it to be soluble under awider variety of conditions is disclosed in U.S. application Ser. No.09/994,998, filed Nov. 27, 2001, the contents of which are incorporatedherein by reference.

Polymerizations of the present invention can be carried out under a widevariety of conditions. The pH is often between about pH 1.0 and about pH12.0, typically between about pH 6.0 and about pH 11.0. The temperatureis above about 0° C., such as between about 0° C. and about 45° C. orbetween about 15° C. and about 30° C. (e.g., room temperature). Thesolvent can be aqueous (preferably buffered), organic, or a combinationthereof. Organic solvents are typically polar solvents such as ethanol,methanol, isopropanol, dimethylformamide, dioxane, acetonitrile, anddiethyl ether. The concentration of monomer or comonomers is typically0.001 M or greater. Also, the concentration of buffer is typically 0.001M or greater.

Polymerizations of the invention use a catalytic amount of one of theenzymes or enzyme mimetics described above, which can be between aboutone unit/mL and five units/mL, where one unit will form 1.0 mgpurpurogallin from pyrogallol in 20 seconds at pH 6.0 at 20° C.Preferably, the enzyme or enzyme mimetic is added to the solution afteraddition of the antioxidant monomer or comonomers. A peroxide is thenadded incrementally to the reaction mixture, such as not to de-activatethe enzyme or enzyme mimetic, until an amount approximatelystoichiometric with the amount of antioxidant monomer or comonomers hasbeen added.

Although the enzyme or enzyme mimetic is responsible for formation ofphenol-based free radicals needed for chain propagation, the coupling ofradicals to form a polymer chain is controlled by the phenoxy radicaland solvent chemistries. Further details regarding the coupling ofphenoxy radicals can be found in “Enzymatic catalysis in monophasicorganic solvents,” Dordick, J. S., Enzyme Microb. Technol. 11:194-211(1989), the contents of which are incorporated herein by reference.Coupling between substituted benzene monomers typically occurs orthoand/or para to a hydroxyl group. Coupling rarely occurs meta to ahydroxyl group.

Polymerization preferably results in the formation of C—C bonds.Preferred polymers will contain at least about 95% C—C bonds, at leastabout 90% C—C bonds, at least about 80% C—C bonds, at least about 70%C—C bonds, at least about 60% C—C bonds or at least about 50% C—C bonds.Especially preferred polymers contain about 100% C—C bonds.

Antioxidant polymers of the present invention can be present in a widevariety of compositions where free radical mediated oxidation leads todeterioration of the quality of the composition, including edibleproducts such as oils, foods (e.g., meat products, dairy products,cereals, etc.), and other products containing fats or other compoundssubject to oxidation. Antioxidant polymers can also be present inplastics and other polymers, elastomers (e.g., natural or syntheticrubber), petroleum products (e.g., fossil fuels such as gasoline,kerosene, diesel oil, heating oil, propane, jet fuel), lubricants,paints, pigments or other colored items, soaps and cosmetics (e.g.,creams, lotions, hair products). The antioxidant polymers can be used tocoat a metal as a rust and corrosion inhibitor. Antioxidant polymersadditionally can protect antioxidant vitamins (Vitamin A, Vitamin C,Vitamin E) and pharmaceutical products from degradation. In foodproducts, the antioxidant polymers will prevent rancidity. In plastics,the antioxidant polymers will prevent the plastic from becoming brittleand cracking.

Antioxidant polymers of the present invention can be added to oils toprolong their shelf life and properties. These oils can be formulated asvegetable shortening or margarine. Oils generally come from plantsources and include cottonseed oil, linseed oil, olive oil, palm oil,corn oil, peanut oil, soybean oil, castor oil, coconut oil, saffloweroil, sunflower oil, canola (rapeseed) oil and sesame oil. These oilscontain one or more unsaturated fatty acids such as caproleic acid,palmitoleic acid, oleic acid, vaccenic acid, elaidic acid, brassidicacid, erucic acid, nervonic acid, linoleic acid, eleosteric acid,alpha-linolenic acid, gamma-linolenic acid, and arachidonic acid, orpartially hydrogenated or trans-hydrogenated variants thereof.Antioxidant polymers of the present invention are also advantageouslyadded to food or other consumable products containing one or more ofthese fatty acids.

The shelf life of many materials and substances contained within thematerials, such as packaging materials, are enhanced by the presence ofan antioxidant polymer of the present invention. The addition of anantioxidant polymer to a packaging material is believed to provideadditional protection to the product contained inside the package. Inaddition, the properties of many packaging materials themselves,particularly polymers, are enhanced by the presence of an antioxidantregardless of the application (i.e., not limited to use in packaging).Common examples of packaging materials include paper, cardboard andvarious plastics and polymers. A packaging material can be coated withan antioxidant polymer (e.g., by spraying the antioxidant polymer or byapplying as a thin film coating), blended with or mixed with anantioxidant polymer (particularly for polymers), or otherwise have anantioxidant polymer present within it. In one example, a thermoplasticsuch as polyethylene, polypropylene or polystyrene is melted in thepresence of an antioxidant polymer in order to minimize its degradationduring the polymer processing. An antioxidant polymer can also beco-extruded with a polymeric material.

An alkyl group is a saturated hydrocarbon in a molecule that is bondedto one other group in the molecule through a single covalent bond fromone of its carbon atoms. Examples of lower alkyl groups include methyl,ethyl, n-propyl, iso-propyl, n-butyl, sec-butyl and tert-butyl. Analkoxy group is a substituted or unsubstituted alkyl group where anoxygen atom connects the alkyl group and one other group. An acyl groupis a substituted or unsubstituted alkyl group that contains a terminalcarbonyl moiety.

Aryl groups include carbocyclic aryl groups such as phenyl, 1-naphthyl,2-naphthyl, 1-anthracyl and 2-anthracyl, and heterocyclic aryl groupssuch as N-imidazolyl, 2-imidazole, 2-thienyl, 3-thienyl, 2-furanyl,3-furanyl, 2-pyridyl, 3-pyridyl, 4-pyridyl, 2-pyrimidyl, 4-pyrimidyl,2-pyranyl, 3-pyranyl, 3-pyrazolyl, 4-pyrazolyl, 5-pyrazolyl,2-pyrazinyl, 2-thiazole, 4-thiazole, 5-thiazole, 2-oxazolyl, 4-oxazolyland 5-oxazolyl.

Aryl groups also include fused polycyclic aromatic ring systems in whicha carbocyclic aromatic ring or heteroaryl ring is fused to one or moreother heteroaryl rings. Examples include 2-benzothienyl, 3-benzothienyl,2-benzofuranyl, 3-benzofuranyl, 2-indolyl, 3-indolyl, 2-quinolinyl,3-quinolinyl, 2-benzothiazole, 2-benzooxazole, 2-benzimidazole,2-quinolinyl, 3-quinolinyl, 1-isoquinolinyl, 3-quinolinyl, 1-isoindolyland 3-isoindolyl.

Examples of suitable substituents on an alkyl, aryl or acyl group mayinclude, for example, halogen (—Br, —Cl, —I and —F), —OR_(a), —CN, —NO₂,—N(R_(a))₂, —COOR_(a), —CON(R_(a))₂, —SO_(k)R_(a) (k is 0, 1 or 2) and—NH—C(═NH)—NH₂. An alkyl group can also have ═O or ═S as a substituent.Each R_(a) is independently —H, an alkyl group, a substituted alkylgroup, a benzyl group, a substituted benzyl group, an aryl group or asubstituted aryl group. A substituted benzylic group or aryl group canalso have an alkyl or substituted alkyl group as a substituent. Asubstituted alkyl group can also have a benzyl, substituted benzyl, arylor substituted aryl group as a substituent. A substituted alkyl,substituted aryl or substituted acyl group can have more than onesubstituent.

The following examples are not intended to be limiting in any way.

EXEMPLIFICATION EXAMPLE 1 Preparation ofpoly(2-tert-butyl-4-hydroxyanisole)

Horseradish peroxidase-catalyzed polymerization of2-tert-butyl-4-hydroxyanisole (2-BHA) was carried out according to theprocedure of Holland, H. L. , in Organic Synthesis with OxidativeEnzymes, VCH Publishers, Inc., 1992, the contents of which areincorporated herein by reference. Briefly, 2-BHA (100 mg, 0.56 mmol) wasadded to a 1:1 (v/v, 6 mL) solution of methanol and 0.01 M sodiumphosphate buffer (pH 7), along with horseradish peroxidase, at roomtemperature. The polymerization was initiated by incremental addition ofa stoichiometric amount of hydrogen peroxide (5% aqueous solution, 35microliters, 0.56 mmol) over a period of 3 hours. After completeaddition of the hydrogen peroxide, the reaction was allowed to continuefor another 24 hours. The solvent was evaporated by freeze-drying. Thepolymer was washed thoroughly with aqueous methanol (1:1 v/v) to removethe enzyme and phosphate salts, followed by drying under vacuum.

The 500 MHz ¹H NMR spectra of monomeric and polymeric 2-BHA are shown inFIGS. 1 and 2, respectively. The NMR spectrum of the polymer shows clearchanges from that of the monomer, such as the methoxy proton changingfrom a single peak at 3.7 ppm to a distribution of resonances between3.4 and 3.8 ppm, which corresponds to the molecular weight of thepolymer product. The distribution of molecular weights observed in theMALDI-TOF-MS spectrum (FIG. 3) also confirms formation of a polymer. A¹³C spectrum of poly(2-BHA) showed new peaks at 115.5, 116.2, 138.2 and148.2 ppm, which suggests the presence of C—C and C—O—C couplings in thepolymer (data not shown). Thermogravimetric analysis (TGA) profiles(FIG. 4) of 2-BHA showed there was about 15% mass loss up to about 125°C. and TGA of poly(2-BHA) showed there was about 15% mass loss up toabout 275° C., which indicates a considerable improvement in thermalstability for the polymer.

EXAMPLE 2 Preparation of Poly(tert-butyl-hydroxyquinone)

Poly(tert-butyl-hydroxyquinone) was prepared by a variation of themethod described in Example 1. The distribution of molecular weightsobserved in the MALDI-TOF-MS spectrum (FIG. 5) confirms formation of apolymer.

EXAMPLE 3

Comparison of Antioxidant Activity of Monomers Versus Polymers

The antioxidant activity of monomers and enzymatically-preparedpolymeric antioxidants was compared by measuring the bleaching of abeta-carotene system. In the model system, beta-carotene undergoes rapiddiscoloration in the absence of an antioxidant. The assay andmeasurements were conducted according to the procedure described inJayaprakasha, G. K. , et al. Food Chemistry 73: 285-290 (2001) andHidalgo, M. E., et al Phytochemistry 37: 1585-1587 (1994), the contentsof which are incorporated herein by reference. Briefly, beta-carotene(0.2 mg), linoleic acid (20 mg), and 200 mg of Tween-40 (polyoxyethylenesorbitan monopalmitate) were dissolved in 0.5 mL of chloroform. Thechloroform was removed under vacuum and the resulting mixture wasimmediately diluted with 10 mL of distilled water and mixed well for 1-2minutes. The resulting emulsion was further made up to 50 mL withoxygenated water. Aliquots (4 mL) of the emulsion were mixed with 0.2 mLof test sample (monomer or polymer) in dimethylformamide (DMF), so thatthere were 100 ppm of monomer or polymer present in the aliquot. Acontrol was prepared by mixing 0.2 mL of DMF with 4 mL of the aboveemulsion. The samples were incubated at 50° C. The absorbance of allsamples at 470 nm was taken initially (t=0) and continued up to 180minutes at 15 minute intervals. Data from the assay of 2-BHA and itspolymer are shown in FIG. 6. Antioxidant activity is calculated based onthe formula:Antioxidant Activity=100 (1−(A _(o) −A _(t))/(A ¹ _(o) −A ¹ _(t))),

-   -   A_(o)=absorbance of the test sample at zero time,    -   A¹ _(o)=absorbance of the control at zero time,    -   A_(t)=absorbance of the test sample at time t (180 min), and    -   A¹ _(t)=absorbance of the control at time t (180 min).

The results for several monomer-polymer pairs are shown in the followingtable:

Monomer Polymer % Increase in Compound Activity Activity PolymerActivity 2-tert-butyl-4- 44.24 53.74 21.5 hydroxyanisole tert-butyl-5.77 9.7 68.1 hydroxyquinone 4-azophenylphenol 5.4 25.5 372 phenol 2.110.0 376 3-hydroxybenzyl alcohol 1.0 5.0 400 4-methylphenol 0.9 5.0 455

EXAMPLE 4

Antioxidant Activity of Monomer Versus Polymer

The antioxidant activity of several other antioxidant monomer/polymerpairs were determined by the procedure described in Example 3.

% Antioxidant Activity % Antioxidant Activity Compound of Monomer ofPolymer 3-Hydroxybenzyl 1.0 5.0 alcohol 4-Methylphenol 0.9 5.0 Phenol2.1 10.0 4-Azophenylphenol 5.4 25.5

EXAMPLE 5

Stability of Cooking Oils

Corn and canola oils were blended with amounts oftert-butyl-hydroxyquinone (TBHQ) and poly(TBHQ), such that theconcentration of phenol moieties was equal. The oils were heated tofrying temperature (190° C.) and their oil stability index was measured.The oil stability index (American Oil Chemists' Society Cd 126-92)measures the amount of time before the oil begins to rapidly oxidize. Agreater length of time indicates an oil with a greater antioxidantcapacity, which likely corresponds to a longer potential shelf life.

Oil Control TBHQ Poly(TBHQ) Canola 7.8 hours 10.8 hours 19.2 hours Corn3.6 hours  6.6 hours  9.0 hours

The above table shows that polymerized TBHQ is more effective inpreventing oxidation of the oils, as compared to monomeric TBHQ. BothTBHQ and poly(TBHQ) are significantly more stable than oil without anadded antioxidant.

EXAMPLE 6

Safety of Antioxidant Polymers

A study was conducted based upon the standards of OECD Guidelines forTesting of Chemicals, OECD 423. Ten Sprague-Dawley albino rats wereadministered with 2000 mg/kg body weight poly(TBHQ) as a single dose viagastric gavage. After administration, the animals were returned to theircages and observed for signs of toxicity for up to 14 days. Body weightswere determined prior to dosing and on the day of death or prior toterminal sacrifice. A second study was performed using three female ratswith 500 mg/kg body weight of poly(TBHQ).

Three of the five female rats administered with 2000 mg/kg poly(TBHQ)died prior to completion of the study. All animals manifested clinicalsigns of toxicity including piloerection, nasal discharge,chromodacryorrhea and lethargy. In the animals that did not survive 14days, the intestines were inflamed. None of the surviving animals showedabnormal signs at gross necropsy. The three rats administered with 500mg/kg poly(TBHQ) survived the duration of the study and did not manifestany clinical signs of toxicity.

Based on this study, the oral LD50 of poly(TBHQ) was determined to bebetween 500 mg/kg and 2000 mg/kg. For comparison, the oral LD50 ofsodium chloride is about 3000 mg/kg and the oral LD50 of sodium cyanideis about 4 mg/kg. Thus, poly(TBHQ) has a relatively low toxicity torats.

Equivalents

While this invention has been particularly shown and described withreferences to preferred embodiments thereof, it will be understood bythose skilled in the art that various changes in form and details may bemade therein without departing from the scope of the inventionencompassed by the appended claims.

1. A method of inhibiting oxidation of a substance, comprising the stepof contacting said substance with a polymer that includes repeat unitsrepresented by one or both of Structural Formula (I) and StructuralFormula (II):

wherein: R is —H or a substituted or unsubstituted alkyl, acyl or arylgroup; Ring A is substituted with at least one tert-butyl group orsubstituted or unsubstituted n-alkoxycarbonyl group, and optionally oneor more groups selected from the group consisting of —OH, —NH, —SH, asubstituted or unsubstituted alkyl or aryl group, and a substituted orunsubstituted alkoxycarbonyl group; and Ring B is substituted with atleast one —H and at least one tert-butyl group or substituted orunsubstituted n-alkoxycarbonyl group, and optionally one or more groupsselected from the group consisting of —OH, —NH, —SH, a substituted orunsubstituted alkyl or aryl group, and a substituted or unsubstitutedalkoxycarbonyl group; n is an integer equal to or greater than 2; and pis an integer equal to or greater than
 0. 2. The method of claim 1,wherein Ring A and Ring B are each substituted with at least onetert-butyl group.
 3. The method of claim 2, wherein the polymer includesrepeat units represented by one or both of Structural Formula (III) andStructural Formula (IV):


4. The method of claim 3, wherein the polymer further includes repeatunits represented by one or more of Structural Formulas (Va), (Vb),(Vc), (VIa), (VIb) and (VIc):

wherein R₁, R₂ and R₃ are independently selected from the groupconsisting of —H, —OH, —NH, —SH, a substituted or unsubstituted alkyl oraryl group, and a substituted or unsubstituted alkoxycarbonyl group,provided that at least one of R₁, R₂ and R₃ is a tert-butyl group; and jand k are independently integers of zero or greater, such that the sumof j and k is equal to or greater than
 2. 5. The method of claim 4,wherein R is —H or —CH₃.
 6. The method of claim 5, wherein R₂ is —H, —OHor a substituted or unsubstituted alkyl group.
 7. The method of claim 1,wherein the polymer includes repeat units selected from the groupconsisting of:


8. The method of claim 7, wherein the polymer consists of repeat unitsselected from the group consisting of: